Laser peening is a novel surface treatment technique for improving the mechanical properties of metal parts' surface. To investigate and evaluate the effect of laser peening on the microstructural ...changes, texture evolution, and residual stress distribution changes, laser peening experiment was undertaken using Nd:YAG laser system with the pulse–width of 20ns and max pulse–energy of 9J. Micro-hardness measurements of the untreated and treated specimens were carried out with Vickers indenter. Depth-resolved characterization of the residual stresses and strains was achieved using X-ray diffraction. The structure–texture–phase–stress combined analysis was performed based on the X-ray diffraction patterns using the whole pattern fitting method. The relationship between laser peening processing parameters, microstructure, texture, residual stress distribution and hardness are presented and discussed. The results showed that laser peening could improve microstructures and properties of TiAl alloy.
•Evidence of inter-lamellar slip in TiAl is caused by laser peening.•Composite-like microstructure increases with laser peening energy.•Laser peening introduces strong harden in TiAl alloy.•A number of orientation maxima and minima were induced by laser peening.•The highest compressive residual stress appeared in sub-surface.
Based on the effect of confinement media and ablative coating, laser shock processing (LSP) is a surface modification processing with properties of high efficiency, cleaning, and non-pollution. At ...room temperature, water is used as the common confinement media and black tape is used as ablative coating in LSP. However, due to the instability of water and black tape at high temperature, warm laser shock processing (WLSP) favors silicone oil as confinement media and aluminum foil as ablative coating, where aluminum foil is pasted on specimen surface by thin vacuum grease. Due to the differences in confinement media and ablative coating, this work focuses on the effect of confinement media and ablative coating on surface quality and mechanical property of FGH98 powder material treated by LSP. FGH98 specimens were strengthened by LSP at room temperature with different confinement medias and ablative coatings. Three groups were divided based on confinement media and ablative coating: water+black tape, water+aluminum foil, and silicone oil+aluminum foil. The group of black tape and silicone oil was removed for the absence of practical significance in engineering. 2D and 3D surface topography was observed by white-light interference surface profilometer (WLI). In addition, surface microhardness and compressive residual stress were determined. The results show that a circular pit is induced by LSP, and its shape is similar to the shape of the Gaussian curve. Compared with the other groups, the 2D surface topography of the circular pit section in the silicone oil+aluminum foil group is smoother, which would delay crack initiation. After LSP treatment, surface microhardness is improved by 7.8-10.6%, and compressive residual stress raises from 355MPa to 896MPa in the first group. According to the comparison of residual stress and surface quality, the effect of confinement media and ablative coating groups on laser shock pressure is ranked in order: water+black tape > water+aluminum foil > silicone oil+aluminum foil. The main reasons for that group order are that shock pressure may be consumed by grease cream and the reduced acoustic impedance of silicone oil is lower than that of water.
Fraction of absorbed energy (FAE) is an important parameter to determine the plasma shock wave pressure. With the purpose of obtaining the FAE of material and accurately calculating the plasma shock ...wave pressure, a method based on laser shock processing (LSP) experiment and finite element simulation was proposed in this work. The Ni-based superalloy GH4169 was selected as experimental material, and the experimental sample was treated by single-point LSP. The residual stress of experimental sample after LSP treatment was determined using sin
2
ψ method by X-ray residual stress device. In finite element simulation, the initial value of FAE was assumed as 0.1, and then, the LSP finite element simulation was performed with the change of FAE until the results obtained by LSP experiment and simulation were fell into an allowable range. Based on this method, the FAE with 0.13 for Ni-based superalloy GH4169 was obtained. This work can enrich the theory of LSP and provide theoretical guidance for researchers to obtain the accurate FAE of materials.
In this study, the martensitic stainless-steel powder had been successfully deposited on the surfaces of 1045 wrought steel substrates using five types of laser metal deposition strategies. The ...results showed that a thin buffer layer can be naturally generated in-between the deposition layer and substrate owning to the dilution effect, producing functionally graded structures consisted of martensite dendrite matrices and intermetallic phases (e.g., M23(C, B)6). Unfortunately, the poor deformation characteristic of natural buffer layers can exacerbate the risk of cracking, leading to an incompatibility between martensitic stainless steel and forming steel. A thick artificial buffer layer was then designed by addition of Inconel 625 powder. Because of the formation of graded austenite phase in the artificial buffer layer, the yield strength of specimen was enhanced significantly. Hence, our study can be used for manufacture of reliable moulds with high surface hardness and structural strength and may be helpful in further developing hybrid forming strategy in the field of mould manufacture. When subjected to stress impact during mould filling, the artificial buffer layer with functionally graded properties would have a perfect capability to bear the deformation as the load increased, dramatically improving the reliability and functionality of moulds.
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•The buffer layers was formed due to the dilution effect.•The artificial buffer layer had perfect functionally graded properties.•A hybrid mould with artificial buffer layer was fabricated by LMD.
To improve the accuracy of numerical simulation of laser shock peening, a novel model is developed to predict residual stress distribution. An optical beam measurement system, a white light confocal ...displacement sensor, and other sensors are used to measure the laser shock peening parameters. Based on actual parameters, the model of shock wave pressure spatial distribution is established. Effects of key parameters, viz., overlapping rate and laser beam quality on residual stress distribution are analyzed by the proposed model. The influence mechanism of laser beam quality on residual stress hole is analyzed. Compared with conventional models, it is found that the proposed model has higher precision to predict residual stress distribution. The processing efficiency and strengthening effect can be improved by optimizing the overlapping rate and laser beam quality. The edge gradient of shock wave pressure reduces the intensity of the release wave convergence at the center, which can improve the uniformity of residual stress distribution. The proposed model can not only improve the accuracy of numerical simulation, but also provide guidance for optimizing the laser beam quality.
Since the extreme service conditions, the serious failure problems caused by wear and corrosion are often encountered in the service process for aeronautical components. Laser shock processing (LSP) ...is a novel surface-strengthening technology to modify microstructures and induce beneficial compressive residual stress on the near-surface layer of metallic materials, thereby enhancing mechanical performances. In this work, the fundamental mechanism of LSP was summarized in detail. Several typical cases of applying LSP treatment to improve aeronautical components' wear and corrosion resistance were introduced. Since the stress effect generated by laser-induced plasma shock waves will lead to the gradient distribution of compressive residual stress, microhardness, and microstruture evolution. Due to the enhancement of microhardness and the introduction of beneficial compressive residual stress by LSP treatment, the wear resistance of aeronautical component materials is evidently improved. In addition, LSP can lead to grain refinement and crystal defect formation, which can increase the hot corrosion resistance of aeronautical component materials. This work will provide significant reference value and guiding significance for researchers to further explore the fundamental mechanism of LSP and the aspects of the aeronautical components' wear and corrosion resistance extension.
As a progressive surface-hardening technology, laser shock processing (LSP) can enhance the mechanical properties and extend fatigue life for metallic components through laser-generated high-pressure ...plasma shock waves. In this work, LSP was used to treat titanium alloy Ti-13Nb-13Zr experimental coupons, and the microstructural response and surface mechanical properties of the Ti-13Nb-13Zr experimental coupons were investigated. After the LSP treatment, the X-ray diffraction (XRD) peaks were shifted without any new phase formation. The surface roughness of the experimental coupons increased, which can be explained by the LSP-induced severe plastic deformation. The LSP treatment effectively enhanced the surface compressive residual stress of Ti-13Nb-13Zr. Meanwhile, the microhardness of the Ti-13Nb-13Zr was also obviously increased after the LSP treatment. The experimental results also showed that the number of shocks times is an important factor in the improvement of surface mechanical properties. LSP treatment with multiple shocks can lead to more severe plastic deformation. The surface roughness, surface compressive residual stress and microhardness of the Ti-13Nb-13Zr experimental coupons shocked three times are higher than those after one shock. What is more, grain refinement accounts for the mechanical properties' enhancements after the LSP treatment.
Tool wear introduced during grinding nickel-based superalloys was identified as a significant factor affecting the production quality of aero-engine industries concerning high service performance and ...high precision. Moreover, uncertainties derived from the various cooling-lubrication modes used in grinding operations complicated the assessment of grinding preformation. Therefore, this work investigated the tool wear mechanisms in grinding nickel-based superalloys that adopted five cooling-lubrication modes and investigated how the wear behaviors affected grinding performance. Results showed that chip-deposits covered some areas on the tool surface under dry grinding and accelerated the tool failure, which produced the highest values of tangential force, 7.46 N, and normal force, 14.1 N. Wedge-shape fractures induced by indentation fatigue were found to be the predominant wear mechanism when grinding nickel-based superalloys under flood cooling mode. The application of minimum quantity lubrication-palm oil (MQL-PO), MQL-multilayer graphene (MQL-MG), and MQL-Al
O
nanoparticles (MQL-Al
O
) formed lubricity oil-film on the tool surface, which improved the capacity of lubrication in the tool-workpiece contact zone and provided 37%, 30%, and 52% higher coefficient of friction than dry mode, respectively. The results of this study demonstrate that lubricated oil-film produced by MQL modes reduces the possibility of fractures of cubic boron nitride (CBN) grits to some extent.
As the microporous structure has been widely used in the field of precision machining, at the same time, the requirements for the quality of microporous machining are continuously increasing. Water ...jet-guide laser processing technology (WJGL) has been gradually applied for its high machining precision. However, there are a few researches on the heat conduction process of WJGL processing metal materials. Therefore, it is of great significance to study the transient thermal effect of metal materials and the mechanism of material removal to improve the processing quality. In order to explore the heat conduction model of WJGL processing metal materials, this paper is based on the "element birth and death" technique in the finite element method, and the three-dimensional transient temperature field of four typical metal materials (titanium alloy, stainless steel, aluminum alloy, copper) and material removal model are established. Under this model, the removal mechanism of different metal materials and the influence of different process parameters on the temperature field distribution of the material are studied, and the influence of fixed-position drilling and helix drilling on the microporous morphology is compared. The results show that copper and aluminum alloys can obtain a larger depth-to-diameter ratio and a smaller hole taper. Titanium alloy and stainless steel have better hole roundness, lower hole edge temperature, and smaller thermal deformation. Hole roundness error and hole taper decrease with the increase of laser power. The roundness error of each material is reduced to within 10 μm when the laser power is 10 W, and the average hole taper is 8.73°.
In order to study the effect of laser peening on microstructures and properties of TiAl alloy, TiAI alloy samples were treated by Nd：YAG laser system with the wavelength of 1064 nm, pulse-width of 18 ...ns, and pulse-energy of 0-10J. Surface micro-hardness, roughness, and microstructural characteristics were tested with micro-hardness tester, roughness tester and scanning electron microscope. Residual stress and pole figures were tested with X-ray diffraction and its high-temperature stability was analyzed. The experimental results show that surface micro-hardness increases by up to 30%, roughness increases to 0.37 lain, compressive residual stress increases to 337 MPa, and local texture and typical lamellar microstructure are generated. Residual stress, micro-hardness, and （002） pole figures tests are conducted, compressive residual stress value drops from 337 MPa to 260 MPa, hardness value drops from 377 HV0.2 to 343 HV0.2, and the （002） poles shift back to the center slightly. Laser peening improves microstructure and properties of TiAl alloy significantly.
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